Film-Tech Forum ARCHIVE: Suggestions for motors suitable for motorising rewinds?

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Posted by David Rigby (Member # 1301) on 09-17-2003, 09:57 AM:

Anyone have any pointers on motors suited for this task (and ideally where to acquire them? (ideally in the UK due to shipping cost)

I guess a motor from a scrap film tower would do the job, though ideally it should be single phase and reversible. It must be able to wind 2000m (say 7000 feet) of film easily - would 1/4KW do the trick? Any tips / suggestions appreciated [Smile]

David

Posted by Leo Enticknap (Member # 534) on 09-17-2003, 10:19 AM:

I once saw a homebrew motorised rewind at a little fleapit on the south Devon coast. The motor chassis was bolted to the bench and linked to the rewind head by a toothed belt pulley arrangement. The motor had apparently been removed from a dead washing machine (its drum bearings had failed). This rig didn't look like it was intended to wind anything bigger than 2,000 feet, though.

So if you can manage to find a dead washing machine with a live motor, I guess it might do the job...

Posted by Greg Mueller (Member # 17) on 09-17-2003, 10:27 AM:

I would suggest a 90 VDC motor. With V-belt reduction and a motor speed controller unit. All of these can be had surplus for pretty cheap. Using a DC motor allows you to reverse direction easily and using a 90 volt model is cheaper (for the controller) than the 24 or 12 volt units.

Posted by John Pytlak (Member # 331) on 09-17-2003, 08:14 PM:

I likewise suggest using a variable speed motor, so you can control acceleration. Having a motor that goes from "0 to 60" instantly is very likely to cinch, stretch, or even break film, and makes winding tension hard to control. Likewise, as you near the end of the winding, it's nice to slow down so the film end doesn't slap wildly.

Posted by Philippe Laude (Member # 79) on 09-18-2003, 05:09 AM:

Like Greg and John, I suggest a DC motor, with permanent magnet. This gives a maximum torque even at low speed.
My best "buy" is the POLYMOTOR ITALIA that you'll find on any PHILIPS washing machine. He's very versatile and dependable, able to work under 12V to 220V, revving from 2000 RPM to 20.000 RPM. Here in Belgium you can get it in every scrape yards for a few bucks (Euros).

Philippe

Posted by David Rigby (Member # 1301) on 09-18-2003, 09:05 AM:

Thanks guys. I'd figured on a fixed speed motor with a speed control and a 220/240V AC gear motor had originally been suggested for this application (no need for a DC supply). Is this unnecessarily expensive and/or mechanically tricky?

David

Posted by Greg Mueller (Member # 17) on 09-18-2003, 12:27 PM:

Another factor to consider is final RPM. A higher speed motor will require more reduction to get to a usable speed. With a speed controller you can go pretty slow or pretty fast. With any kind of fixed speed unit, you're going to be rewinding film REAL fast. Guess I'm a control freak, eh?

Posted by Philippe Laude (Member # 79) on 09-19-2003, 01:52 AM:

See (Pictures, Philippe Laude's private screening room)another use of the POLYMOTOR in my booth: Driving the tower.
The motor is supplied with a 50V transformator, a KEMO speed control and a small bridge diode. Maximum cost of all this, second hand:100€.
David, that cheap (max 25€) KEMO speed control is only useful for motors with brushes.If you intend to use a brushless AC motor, you'll need to use an expensive frequency converter.

Posted by David Rigby (Member # 1301) on 09-22-2003, 10:26 AM:

Thanks for the reply Philippe. VERY nice homemade tower you have there. I'd like to wind up with something like that myself eventually but as I have no access to engineering tools, it means paying someone else to do the job for me.

Is this POLYMOTOR likely to be the same as the one you used?

POLYMOTOR on Ebay

Still digging, as you can tell!

David

Posted by Philippe Laude (Member # 79) on 09-23-2003, 01:31 AM:

David,

Yes it is! You seem to be in your lucky day! The "startpreis" is low and I'm confident it'll remain, for that item isn't much sought after. Buy it, even if you have to pay 15€ for it!

From the picture it seems it's equipped with a "Poly V" pulley, this means you'll have to use a "Poly V" belt, easy to find, supple and dependable, but maybe you'll experience difficulty in finding a "Poly V" driven pulley. If you don't find one, use a common V-belt and V pulleys.